The present invention relates to an exposure apparatus and method, and a device manufacturing method. The present invention is particularly suitable for an immersion exposure apparatus.
A projection exposure apparatus has been conventionally used to manufacture fine devices, such as a semiconductor memory and a logic circuit, using the photolithography technology. The projection exposure apparatus projects a circuit pattern of a reticle (mask) onto a wafer via a projection optical system. The current mainstream is step-and-scan exposure apparatus (scanner) that exposes by scanning the reticle and the wafer relative to each other.
As the high integration or fine processing of the semiconductor device (circuit pattern) proceeds, the demands for the specification and performance of the projection optical system become increasingly stricter. In general, use of a short wavelength of the exposure light and a high numerical aperture (“NA”) scheme of the projection optical system are effective for high resolving power. For the high NA scheme, a recently proposed optical system achieves a NA of 1 or greater through the immersion lithography that fills liquid in a space between the wafer and the final optical element of the projection optical system closest to the wafer.
On the other hand, one proposed approach to use a short wavelength of the exposure light is realized through use of an ArF excimer laser (having a wavelength of about 193 nm) and a F2 laser. When this type of laser is used for a light source, a usable glass material is limited to quartz and calcium fluoride (CaF2) in a dioptric optical system, due to a transmittance degradation of the glass material to the exposure light. In addition, even with this type of glass material, a small dispersion difference makes very difficult a correction of a chromatic aberration in an optical system having a very high NA. Accordingly, various proposals that include a mirror in the optical system are made to avoid the problems of the transmittance and the chromatic aberration. For example, a catadioptric projection optical system that combines a reflection system and a refraction system is disclosed. See Japanese Patent Application, Publication No. (“JP”) 2005-37896.
The exposure apparatus is also required to inexpensively improve the throughput or productivity. However, a large aperture glass material associated with the high NA scheme causes a cost increase. In particular, the catadioptric projection optical system has a rectangular slit shaped exposure area that does not generally contain the lens's optical axis, requiring a larger view angle than the dioptric optical system. Thereby, a large aperture of the lens diameter is likely to increase the cost. Moreover, the large aperture of the lens's diameter makes difficult or unavailable the aberrational correction or the so-called lens design itself in addition to the cost increase.
For the improvement of the productivity, one exposure apparatus preferably exposes a wide variety of semiconductor devices, or differently sized chips. Accordingly, the conventional scanner includes a large aperture lens in the projection optical system, makes the longitudinal direction of the exposure area (orthogonal to the scanning direction) variable for various sized chips. However, as described above, the large aperture lens causes a cost increase, and the accumulated exposure dose in the exposure area maintains even when the length in the longitudinal direction is made variable. Hence, a time period necessary to expose one chip or shot on the wafer (that is a substrate to be exposed) is always constant. In other words, the conventional scanner maintains the exposure time period whether exposing a small sized chip or a large sized chip.